1. Field of the Invention
The present invention relates generally to a telephony system and more specifically to a virtual private branch exchange (PBX) system for a packet-switching network (PSN).
2. Discussion of the Background
A PBX is an automatic telephone switching system that enables users within an organization to place calls to each other without having to access a public switched telephone network (PSTN). Users can also place calls to outside numbers via the PBX. PBXs are typically located on the premises of a customer and provide a great deal of control and flexibility in the customer's communications. PBXs are well known and are described, for example in Stallings, “Data and Computer Communications,” 4th Edition, MacMillan Publishing Co New York, 1994 which is incorporated herein by reference.
One approach to implementing a PBX involves a virtual PBX call processing method in which a packet switching system establishes a virtual circuit between each distinct pair of user packet stations in a group. The user packet stations exchange signaling packets via the virtual circuits and respond to such packets by coordinating the initiation and disconnection of voice, data, or image calls. All call processing, including the provision of features, such as call forwarding and automatic call back, is accomplished by the stations without the aid of the switching system. Thus, all of the intelligence of the system is on the terminal side of the system and not on the network side. Consequently, telephony agents and terminals are required to process inbound and outbound calls and perform routing. No dynamic tracking of locations is performed by this system, and all of the terminal locations are static.
Methods of using Internet based communication standards for telephone communication have been developed for use with conventional PBXs. These methods simply (1) permit remote telephone access to an existing PBX system via a PSTN and (2) link Internet Protocol (IP) telephony clients to an existing PBX system via an H.323 gateway. H.323 is an ITU (International Telecommunications Union) standard that provides a set of specifications for equipment and services for use with multimedia communications over a network. An example of how IP telephony clients are linked to an existing PBX system via an H.323 gateway is described in quicknet.net/support/AppNotes/AN00004.htm, which is incorporated herein by reference. However, such systems still incorporate a conventional PBX, which handles call referencing and switching.